The diesel engine based vehicles have become more popular for both passenger cars as well as for heavy vehicles for transportation and other applications. However, it is well known fact that these engines emit large amount of hydrocarbons (HCs), carbon monoxide, NOx and particulate matter (PM) due to incomplete combustion of fuel and other processes at higher temperature in internal combustion diesel engines. Due to the concern about the environmental pollution and stringent emission regulations, there is a need to control the emission of these pollutants like NOx, CO and unburnt hydrocarbons (HCs). Oxidation catalysts have been used to oxidize CO, HC and NOx to clean up the diesel engine exhaust. Noble metal based catalysts, particularly Pt and Pd supported on alumina have been used as DOC for oxidation of hydrocarbon and CO to CO2 as well as oxidation of NOx to NO2 which is used for the oxidation of particulate matter. Sometimes, the diesel engine exhaust contains large quantity of SO2 due to the higher sulfur content in the diesel fuel, because of which the noble metal based catalysts gets deactivated due to sulfur poisoning. The diesel engine exhaust temperature sometimes exceeds >600° C., particularly for heavy vehicle diesel engine, and then in the Pt, Pd based catalysts where the Pt, Pd, are dispersed on high alumina support, get agglomerated/sintered thus lowering the catalytic activity of the diesel oxidation catalysts.
WO 2009/074308 or EP 2070581 A1 relates to a catalyst containing a carrier and a coating, characterized in that the coating comprises a support material and at least one zeolite, the support material comprising platinum, palladium and at least one promoter selected from the group consisting of Mg, Ca, La, Ti, Zr, Hf, Au, Si, Sn, P compounds or mixtures of these promoters, loaded thereon. The document also relates to a process for the manufacture of the catalyst and the use thereof for the purification of exhaust gases from Diesel and lean Otto engines. The catalyst effectively oxidizes carbon monoxide and hydrocarbons, has a high resistance towards hydrothermal aging and is stable during operation.
EP1925362, US2008/0124514, U.S. Pat. Nos. 7,517,826 and 7,534,738 disclose diesel oxidation catalysts in which there is a mixture of a first and a second catalytically active material. For production of the first catalytically active material, palladium in addition to gold is supported on a lanthanum oxide-stabilized aluminum oxide. As the second catalytically active material, platinum is applied, optionally together with palladium or bismuth, to lanthanum oxide-stabilized aluminum oxide. The two catalytically active materials may be applied to an inert honeycomb as a homogeneous powder mixture in E catalytically active layer or in the form of a plurality of different coatings (for example as a Zone catalyst or layer catalyst). In the case of multilayer catalysts, it is additionally possible for Zeolite containing intermediate layers and/or layers comprising palladium supported on cerium oxide to be present.
WO 2009/106849 and US20110113774 disclose diesel oxidation catalysts whose features include high conversion rates for methane and presence of palladium and gold as active components, preferably in alloyed form. For preparation of the catalysts, palladium ex palladium nitrate and gold ex tetrachloroauric acid are applied by precipitation and calcination to aluminum oxide as the support material. The powder component thus obtained can be used to prepare a suspension for coating of conventional flow honeycombs as the catalyst substrate.
WO 2008/117941 discloses diesel oxidation catalysts which feature improved HC oxidation activity and comprise palladium alloyed with gold on aluminum oxide as the first catalytically active material, in addition to platinum alloyed with palladium on aluminum oxide as the second catalytically active material. Instead of aluminum oxide, it is also possible to use other inorganic support oxides, for example silicon dioxide, aluminum silicate, silicates, titanium oxide, Zirconium oxide, SiC and carbon black. A diesel oxidation catalyst produced from the mixture of the catalytically active materials may further comprise oxygen-storing rare earth metal oxides.
US 2008/125308 describe exhaust gas catalysts which comprises a platinum-containing catalyst and a palladium- and gold-containing catalyst, which may additionally comprise Zeolite as an absorbent for hydrocarbons. The two catalysts are arranged in various catalytically active Zones of the exhaust gas catalyst, in such a way that the exhaust gas encounters the platinum catalyst first. This is achieved by means of customary layer or zone arrangement of the two catalysts, or by virtue of the two catalysts being supported on different monoliths.
Article titled, “Cooperative effect of Ce and Mn in MnCe/Al2O3 environmental catalysts” by Hadjiivanov et al. in Appl. Catal. B: Env. 2013, 138-139, 362-372 reports a series of alumina supported catalysts containing Ce and Mn with different ratios for methanol decomposition or NO reduction with methanol decomposition products.
U.S. Pat. No. 6,274,107 discloses an oxidation catalyst, which contains cerium oxide, optionally aluminum oxide and a zeolite, for example zeolite beta. The zeolite can be doped with the metals of the platinum group and other metals or metal species, such as Pt, Rh, Pd, Ru, Os, Ir, Cu, Fe, Ni, Cr, and V. The catalyst promotes the oxidation of CO, HC.
EP 0432534B2 and US 20080279738 disclose a continuously working oxidation catalyst having high conversion performance for hydrocarbons and carbon monoxide in low temperature ranges. The catalyst consists of vanadium compounds and metals of the platinum group, which are applied on aluminum oxide, titanium oxide, silicon oxide, zeolite as well as mixtures thereof. According to Tables 2 and 3 of these documents, the values for the 50% conversion of CO and HC (T50 values which are also termed as light-off temperature) for the freshly prepared catalysts are above 200° C.
U.S. Pat. No. 7,078,004 discloses a method for treating diesel exhaust gas stream whereby the stream is contacted with an upstream catalyst comprising a cerium component and/or a zeolite component and a particulate filter located downstream from the upstream catalyst. The framework alumina of the zeolite component can be substituted by at least one metal selected from the group B, Ga, In, Fe, Cr, V, As. The exchangeable cationic component of the zeolite can be selected from the group consisting of hydrogen and at least one metal selected from the group consisting of Li1 Na, K, Rb, Cs, Mg, Ca1 Sr, Ba1 Cr, Mn1 Fe, Co, Ni, Cu, Nb, Ma, Ta, W, Re, Pt, Pd and Rh.
U.S. Pat. No. 6,093,378 discloses a catalyst composition and structure containing the same and methods for treating diesel exhaust including a catalyst comprising a precious metal on a support, a first zeolite component in the presence of a precious metal and a second zeolite component comprising a zeolite and a precious metal, and a non-catalytic pore-containing zeolite.
US 2013/0202509 relates to a catalytically active material consisting of an inner core (1) and an outer shell (2) surrounding this core, the core being formed from palladium and gold fixed together on a first support oxide, and the shell comprising platinum fixed on a second support oxide, to a diesel oxidation catalyst comprising this catalytically active material, and to an exhaust gas cleaning system comprising this diesel oxidation catalyst.
US 2011/0044871 relates to a coating composition for diesel oxidation catalysts or a combination of diesel oxidation catalysts and diesel particle filters, said coating composition comprising a combination of a noble metal on a metal oxide, with the exception of cerium oxide, and a zeolite doped with iron. The invention also relates to a catalyst provided with the coating and to a method for treating the exhaust gas of diesel internal combustion engines.
U.S. Pat. No. 5,491,120 discloses oxidation catalysts containing ceria and a bulk second metal oxide which may be one or more of titania, Zirconia, ceria-Zirconia, silica, alumina silica and alpha-alumina.
Considering the higher cost of noble metal based catalysts and its deactivation due to sulfur poisoning or sintering effects, development of a non noble metal based catalyst for oxidation of hydrocarbons and CO is highly desired.